Tubular Anode-supported Solid Oxide Fuel Cells

Solid oxide fuel cells(SOFCs) have attract more and more interest due to their highconversion efficiency, low pollution, environmental friendship and fuel flexibility.It isnecessary to develop cost-effective preparation technology of the SOFCs for large-scalecommercialization to instead of the conventional power source. Anode-supported SOFCspossess the advantages of higher mechanical performance, better thermal stability, easiersealing requirement and simpler stack-fabrication process which hava a great applicationpotential among the configurations of SOFCs.Extrusion method was successfully used to fabricate the long tubular anodesupports.YSZ elcetrolyte films were then prepared on the porous anode substrates.LSMcathode was coated on the YSZ film subsequently.The single cell was assembled using silverpaste as sealing and joint material and then tested with humidified hydrogen as fuel.Meanwhile, graphite, starch and corn-powder were added in anode green powder as poreformer.The anode microstructure was then test by SEM. The results showed that the anodestructure using graphite as pore former was more porous and crack-free after sintered.And thecorresponding cells gave the best performance without any charge collector. The maximumpower density of a single cell using graphite as pore former reached241mW·cm-2at800°C,the ohmic impedance was0.7·cm2.Fe(5%molNi) was added in the anode for improving the cell performabce under the samecathod area. SEM reaults showed the coking was decreased in anode structure with Fe addedin Ni.The performance of the single cell reached at400mW·cm-2. AC impedance test resultsshowed that the ohmic impedance was enhanced due to the conductivity of Ni is better thanFe.Dip coating technology was then used to fabricated multilayer anode substrates withgraphite, graphite/starch and starch as pore former, respectively. The results showed that themultilayer structure was more expedient for the cell performace than the unity structure.A phase inversion technique is proposed for fabricating cone-shaped anode supports.Thesingle cell was then assembled and tested with the same procedure.The phase inversiontechnique was experimentized with different quality of NMP. The SEM results showed that the anode structure is more porous and relatively homogeneous with NMP and anode greenpower is1.2:1(weight ratio). The finger-like pores and sponge-like pores was betterdistributed either. The maximum power density of a single cell was180mW·cm-2.Some additives such as PEG-1000, acetone and oleic acid were uesd to improve themicrostructure of the anode. PEG-1000and NMP with a weight ratio of20:100,35:100and50:100were mixed with anode green power and then moulding using phase inversion method,respectively. The results showed that the viscosity of the solvent was changed with additionof PEG-1000. The maximum power density of a single cell reached at340mW·cm-2with PEGand NMP was20:100. The enchancement of the performace due to the extending area of thesponge-like pores. Meanwhile, acetone and oleic acid as additives were also investigated. TheSEM of the anode show that the fingle-like pores extended using acetone as additives and thefingle-like pores and sponge-like pores both vanished using oleic acid.The cone-shaped anode substrates with two opposite sides was successly fabricated indifferent conditions–one side is in contact with coagulant(the corresponding surface is namedas "W-surface"), while the other is isolated from coagulate (I-surface). Single SOFCs weremade with YSZ electrolyte membranes coated on either W-surface or I-surface. Compared tothe cell with YSZ membrane on W-surface, the cell on I-surface exhibits better performance,giving a maximum power density of350mW/cm2at800oC, using wet hydrogen as fuel andambient air as oxidant. AC impedance test results are consistent with the performance. Thesectional and surface structures of the SOFCs were examined by SEM and the relationshipbetween SOFCs performance and anode structure is analyzed. The so-calledsegmented-in-series SOFC was assembled by two single cone-shapped cell.The two-cell-stackprovided an open circuit vlotage of1.8V and the maximum power was2.0W. Structure ofanodes fabricated at different phase inversion temperature is also investigated.The resultshowed that phase inversion temperature at20oC-50oC are suitable for preparing anodesupports.The cone-shapped Ni-GDC anode supports were fabricated by phase inversiontechnology. GDC films were then coated on the anode substrates and LSCF cathode wasperpared subsequently. The structure and performance of single cell was investigated withGDC film sintered at1300,1400,1500oC for4h, respectively. The results showed that the GDC film was porous after1300oC sintered. Compared to1300oC, the porous structure of theGDC film decreased evidently after1400oC sintered. The GDC film was quite dense andcrack-free after1500oC sintered. Oppositely, the anode was coked and the porosity of theanode was not enough. The performance of the single cell also showed that the GDC filmafter1400oC sintered exhibits better performance, the maximum power density at800oC was350mW cm2using wet hydrogen as fuel and ambient air as oxidant.